The present invent on relates to an information recording medium for recording information therein when receiving an energy beam and also to an information recording and reproducing apparatus which uses the information recording medium. More particularly, the present invention concerns an erasable optical disk such as a phase change type optical disk or a magneto-optical disk and also concerns an information recording and reproducing apparatus capable of reproducing information from the erasable optical disk and a read-only optical disk.
This type of technique is disclosed in JP-A-3-272032 in which two metallic layers are provided so that first one of the two first and second metallic layers closer to a recording layer is set to be lower in thermal conductivity than the other second metallic layer, the first metallic layer is disposed as opposed to the second metallic layer, and the recording layer is disposed between the first and second metallic layers.
Further disclosed in a Proceeding of International Symposium on Optical Memory, 1995, pp. 151 and 152 is the fact that a semiconductor thin film of Si or the like material having a large transmittance is used in place of the aforementioned first metallic layer.
In general, reproduction compatibility conditions of the information recording and reproducing apparatus with the read-only optical disk are that the stabilities of tracking servo focusing servo, etc. should be taken into consideration, a medium reflectivity be 15% or more, and the modulation of a reproduced signal be 50% or more when the quality of the reproduced signal is taken into consideration.
Known as one of information recording media satisfying the above conditions is such an information recording medium using a metal such as Au having a high reflectivity as shown in a paper entitled "A CD-compatible erasable disc", by J. H. Coombs, et al., in Proceedings of Topical Meeting on Optical Data Storage, 1994, pp. 94-106. Also known as another information recording medium is an information recording and reproducing system for recording on such an information recording medium, information modulated based on the same modulation system as the read-only optical disk or an information reproducing system therefor. An optical recording disk is disclosed in JP-A-6-76361.